Adsorption mechanism and quantum chemical calculation of six aliphatic VOCs on industrial ZSM-5 zeolites

Abstract

This study focused on the adsorption mechanism of six aliphatic VOCs (cyclohexane, n-hexane, methyl-cyclopentane, n-butanol, butyl-acetate, and methyl-methacrylate) on industrial ZSM-5 zeolites with different Si/Al ratios (20, 50, 300) by combining experiment with theoretical approach. Meanwhile, the effects of flow rate, initial concentration of n-butanol, and temperature for ZSM-5-300 zeolite were investigated. The interaction energy and distribution of the centroid of VOCs on ZSM-5 zeolites were calculated using Material Studio software. The experimental results showed that adsorption capacities of ZSM-5 zeolites for oxygenated VOCs of highly-polarity (n-butanol, methyl-methacrylate, butyl-acetate) were significantly higher than low-polarity VOCs without oxygen (cyclohexane, methyl-cyclopentane, n-hexane). The adsorption efficiency was improved at low temperature, high initial VOCs concentration, and flow rate. The adsorption processes of VOCs on ZSM-5 zeolites were suited to the Freundlich isotherm model and the pseudo-first-order kinetic model. The calculation results revealed that the adsorption capacity increases from about 31 mg/g to 85 mg/g for low-polar VOCs as the adsorption energy decreases from −14.40 kJ/mol to −20.80 kJ/mol. The interaction energy curves of highly-polar VOCs show multiple peaks as the Si/Al ratio decreases, due to they were absorbed in both the intersection and zigzag channels of ZSM-5 framework. The adsorption site distribution indicated that the adsorption preferences were affected by the compatibility between pore geometry and VOCs structure. The ring-structured VOCs were mainly in the intersection channels, and chain-structured VOCs spread across all channels.